Dominance rank, facial morphology, and testes size in male white-faced capuchins: evidence for pre- and post-mating competition

Male reproductive success is determined by the interplay of female mate choice and male-male competition, often linked to dominance rank in social animals. Across taxa, elaborate ornaments, such as bright coloration or large antlers, often function as badges of status, signaling male competitive ability to rivals. In species where females mate with multiple males, post-mating sperm competition also plays an important role in male reproductive success and is associated with larger relative testes size. We investigate the relationship between morphological features and dominance rank in wild male white-faced capuchins. Using parallel-laser photogrammetry, we measured aspects of facial morphology, including facial width-to-height ratio, and testes size. We found that alpha males had significantly larger facial width-to-height ratios, wider faces, and wider scrota than subordinate males. These results suggest that facial traits potentially function as badges of status in male white-faced ca..., We collected data on all males (6+ years old) residing in five habituated groups of white-faced capuchins (Cebus imitator) between January 2021 and May 2024 in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica (SSR). We used parallel-laser photogrammetry (108,109) to noninvasively measure facial features, scrotal width, and body length, of male white-faced capuchins during periods of group stability. For each male, we collected multiple photographs (3 – 5) of their face, body length, and scrotum at least twice per month every three months over both dry and wet seasons. Selected photographs were uploaded in jpeg format to the GIMP GNU image manipulation program (version 2.10.34), a free and open-source image editing program (https://www.gimp.org). We applied GIMP’s standard high contrast filter to each photograph, which enhanced the visibility of the morphological features of interest due to the black and white pelage of the study species. Following Ric..., # Dominance rank, facial morphology, and testes size in male white-faced capuchins: evidence for pre- and post-mating competition

Dataset DOI: [10.5061/dryad.rv15dv4kr](10.5061/dryad.rv15dv4kr)

## Description of the data and file structure

### Files and variables

#### File: Capuchin-Morphology.R

**Description:** We first performed a Principal Component Analysis (PCA) using the principal() function from the ‘psych’ package (115) in R (v4.4.2; 116) and RStudio (v2024.9.1.394; 117) to assess the relationships among facial measurements (facial width, brow width, muzzle width, and facial height) and to check for multicollinearity. Prior to the PCA, we checked for sampling adequacy (Kaiser-Meyer-Olkin test: MSA = 0.66) and sphericity (Bartlett’s test: 𝜒2(6) = 49.75, p < 0.001) to ensure the appropriateness of our data for factor analysis. The data were standardized prior to the PCA using the scale() function, and the PCA analysis was conducted with a varimax rotation to enhance the inter...,

雄性繁殖成功率由雌性择偶与雄性间竞争共同决定，在群居动物中，这类竞争往往与社会优势等级紧密相关。在各类生物类群中，精致的装饰性特征（如鲜亮体色或大型鹿角）常作为地位徽章，向同类竞争者传递雄性的竞争能力。在雌性存在多次交配行为的物种中，交配后精子竞争同样对雄性繁殖成功率起到关键作用，且与更大的相对睾丸体积相关。我们针对野生雄性白面卷尾猴的形态特征与优势等级之间的关联展开研究。采用平行激光摄影测量法（parallel-laser photogrammetry），我们测量了包括面部宽高比在内的面部形态参数以及睾丸尺寸。研究发现，阿尔法雄性（alpha males）的面部宽高比、面部宽度以及阴囊宽度均显著高于从属雄性（subordinate males）。上述结果表明，面部特征可能在雄性白面卷尾猴中承担地位徽章的功能……
我们于2021年1月至2024年5月，在哥斯达黎加瓜纳卡斯特保护区（Área de Conservación Guanacaste）圣罗莎片区（Santa Rosa Sector, SSR），对5个已习惯化的白面卷尾猴（Cebus imitator）种群中所有6岁及以上的雄性个体收集数据。在种群稳定期间，我们采用平行激光摄影测量法（108,109）对雄性白面卷尾猴的面部特征、阴囊宽度以及体长开展非侵入式测量。我们每月至少为每只个体采集3至5张面部、体长及阴囊的照片，且在旱季与雨季中每三个月至少采集两次。筛选后的照片以JPEG格式上传至GIMP GNU图像编辑软件（GIMP GNU image manipulation program，版本2.10.34）——一款免费开源的图像编辑程序（https://www.gimp.org）。我们对每张照片应用GIMP的标准高对比度滤镜，由于本研究物种的被毛为黑白两色，该滤镜可增强目标形态特征的辨识度。后续参考Ric……
# 雄性白面卷尾猴的优势等级、面部形态与睾丸体积：交配前与交配后竞争的证据
数据集DOI: [10.5061/dryad.rv15dv4kr](10.5061/dryad.rv15dv4kr)

## 数据与文件结构

### 文件和变量

#### 文件: Capuchin-Morphology.R

**描述:** 我们首先使用R语言（v4.4.2; 116）及RStudio（v2024.9.1.394; 117）中"psych"包（115）的`principal()`函数开展主成分分析（Principal Component Analysis, PCA），以评估面部测量参数（面部宽度、眉间距、吻部宽度及面部高度）之间的相关性，并检验多重共线性问题。在主成分分析前，我们先检验了采样适配性（Kaiser-Meyer-Olkin检验（Kaiser-Meyer-Olkin test）: MSA = 0.66）与球形度（巴特利特检验（Bartlett’s test）: χ²(6) = 49.75, p < 0.001），以确认数据适用于因子分析。分析前我们通过`scale()`函数对数据进行标准化处理，并采用方差最大旋转（varimax rotation）开展主成分分析以增强……